Study On Shear-Resistance And Its Influence Factors In Different Layers Of Granite Residual Soil

Granite residual soil is distributed widely in the south China, collapse hill and landslide which formed on the granite residual soil are the important types of soil erosion.Granite residual soil is significant inhomogeneity and anisotropy, softening and disintegration, it is a kind of soil which has special structure.Taking typical development, clear layered granite residual soil(surface soil layer, red soil layer, sandy soil layer, detritus layer)in Tongcheng,Hubei province,having undrained triaxial test and direct shear quick shear test, combining soil basic properties of different soil granite residual, the study found that:1、The stress-strain relationship of different layer showed strain hardening model, showed plastic failure, For the same kind of soil, under four kinds of confining pressure, the stress-strain curve spacing are relatively obvious; The stress-strain curve spacing are obvious;The deviatoric stress of the red soil layer and the sandy soil layer has a little change under confining pressure in the early strain, closely related to the strain level; Under the same confining pressure, the deviatoric stress of surface soil layer for destructing is lower, and the deviatoric stress of detritus layer for destructing is higher.Capillary porosity may influence the soil pore pressure to some extent, Rf variation coefficient and capillary moisture capacity extremely significant correlation, The change of capillary porosity may be the reason that affecting the variation of soil Rf, That mutated pore affect the soil Rf to change to some extent.2、Granite residual soil softening is very significant,The internal friction angle and cohesion of the four layers increased,then decreased,the peak of Cohesion appeared at the average water rate 8.11%,The peak of internal friction appeared at the average water rate 11.76%, When the moisture content was about 10%, the granite residual soil may obtain the largest shear strength,when more than a certain water content, With the increase of granite residual soil water content, the strength decreased significantly. Expression of cohesion quickly dissipate, the internal friction angle decreased, significantly reduce of the angle of internal friction is the main reason that lead to the strength to reduce. the Pore development of Granite residual soil, Too much water to disperse soil particles, reducing the contact interaction between particles.3、Under the condition of no significant difference(p<0.05) of the moisture content(average 23.98%), the cohesive force of soil detritus layer is significantly lower than the other three layer, The cohesive force of surface soil layer,Red soil layer and transition layer have no significant difference.The Cohesive force of leaching and detritus layer have a little variation, the variation of red soil layer and sandy soil layer is larger.the variation of internal friction Angle of Four layers is a little, the surface soil layer has the minimum Angle of internal friction, Numerical distribution is relatively concentrated, and the adjacent deposition has no significant difference between layers. Red soil layer of Angle of internal friction in the middle level, Only performance for have significant difference with the detritus layer, this may be due to the sandy soil layer of the particle size distribution, density, cementation, gap conditions were under moderate levels. Sandy soil layer, internal friction Angle, There is no significant difference with the red soil layer, detritus layer of Angle of internal friction, the biggest difference significantly with the other three layers.4、With the soil depth becomes deeper, the Cohesive force increases, then decreases, and the depth of the peak at about 2 m, With the soil depth becomes deeper,The variability of he cohesive force also performed increasing,then decreased.With the soil depth becomes deeper,the Angle of internal friction appear gently increasing trend,The increase of shear strength due to the increase of Angle of internal friction is bigger than the amount of the shear strength reduction due to the contribution cohesive force.5、The main factors which affect the granite residual soil shear strength indexes are water content and sand content.In the case of the soil layer or different soil layer at the outside conditions or structure similar situations, The factors which affect the shear properties of mutation may be saturated hydraulic conductivity, the content of vermiculite, the maximum density variation and soil dry density.Considering the develoing trend of the shear strength of water and sand Content in the meantime:When the water content in a certain range, the shear strength increased with water content increasing and sand content decreased, Overall cohesion increased with the water content decreased, and decreased with increasing sand content, Internal friction angle increased with water content decreased, and increases with the increasing sand content. The reason of the effect of shear strength index concussion is likely to occur mutation of pore gas water pressure, The effect of the soil cement on the granite residual soil affect the shear strength may be overvalued.